A number of naturally occurring acridone alkaloids have been isolated from the family Rutaceae, but only acronycine (1) has been noted for its antitumor activity. (Throughout the specification, compounds will be cross-referenced with underlined numbers to facilitate reading and to avoid repetition of long chemical names). ##STR4##
Acronycine was isolated from the bark of the Australian scrub, Acronychi baueri Schott (Rutaceae) (Hughes, G. K., et al., Nature, 162:223-224 (1948); McDonald, P. L. and A. V. Robertson, Aust. J. Chem., 19: 275-281 (1966); Svoboda, G. H., Lloydia, 29:206-224 (1966)). Experimental studies on acronycine in animals (Finkelstein, T. Z., et al. Cancer Chemother. Reports, 59:975-983 (1975); Schneider, J., et al., J. Med. Chem., 15:266-270 (1972); Svoboda (1966); Svoboda, G. H., et al., J. Pharm. Sci., 55:758-768 (1966); Svoboda, G. H., U.S. Pat. No. 3,985,899, issued Oct. 12, 1976; Svoboda, G. H., U.S. Pat. No. 4,309,431, issued Jan.5, 1982) showed it to be effective against a wide range of neoplasms. Because of its antitumor activity, it has undergone clinical trials (Division of Cancer Treatment. Program Statistics, Mar. 30, 1970, Department HEW, Public Health Service, NIH, IND status filed for acronycine).
Acronycine was found to inhibit the incorporation of extracellular nuclosides into the DNA and RNA of cultured L5178Y cells, but did not interact with DNA (Dunn, B. P., et al. Cancer Res., 33:2310-2319 (1973)). The inhibitory effect of the alkaloid may be the result of an alteration in the transport of uridine through the plasma membrane instead of impaired nucleoside or nucleotide phosphorylation (Dunn, B. P., et al. Cancer Res., 33:2310-2319 (1973)). Similar mechanisms of action were also observed in other studies which indicated that the alkaloid acts primarily on membranous organelles, and its delayed effects may be in part due to interference with the structure, function, and/or turnover of cell-surface components (Tan, P., and N. Auersperg, Cancer Res., 33:2320-2329 (1973)).
Several derivatives of acridinone have been synthesized and tested for their antitumor activity (Liska, K. J., J. Med. Chem., 15:1177-1179 (1972); Radzikowski, C., et al. Arch. Immunol. Ther. Exp., 19:219-228 (1971); Reisch, J. and S. M. E. Aly, Arch. Pharm., 319:25-28 (1986); Schneider, J., et al. J. Med. Chem. 15:266-270 (1972); Svoboda, G. H. Lloydia 29:206-224 (1966)). Of those derivatives synthesized, only O-(dimethylaminoethyl)noracronycine (2) (Reisch, J. and S. M. E. Aly, Arch. Pharm. 319:25-28 (1986)) and 1-nitro-N.sup.10 -substituted acridine-9-ones (3) (Radzikowski, C., et al., Arch. Immunol. Ther. Exp. 19:219-228 (1971)), showed biological activity. Compound 2, bearing a charged dimethyl-aminoethyl side-chain, was reported to exhibit significant antitumor activity (Reisch, J. and S. M. E. Aly, Arch. Pharm. 319:25-28 (1986)). It is possible, therefore, that change of the overall molecular lipophilic-hydrophilic balance and electronic distribution caused by addition of a charged side-chain or nitro function on the molecule of acridine-9-one alter biological activity. ##STR5## Svoboda, G. H., U.S. Pat. Nos. 4,309,431 and 3,985,899, filed Jan. 5, 1982 and Oct. 12, 1976, respectively, teach a method of inhibiting growth of tumor cells using acronycine. However, they do not teach or suggest that other acridone alkaloids may be used to inhibit tumor growth.
To determine structure-activity relationships, the effects of 50 acridone alkaloids on the incorporation of the labeled precursors, [.sup.3 H-methyl]dThd, [5-.sup.3 H]Cyd and [2,3,4,5-.sup.3 H)L-Leu, into DNA, RNA and protein, respectively, were studied. The inhibition by these acridone alkaloids against human leukemic HL-60 cell growth was also studied.